如何使用 System.IO.Abstractions 模拟 FileInfo class？

Question

I have injected the System.IO.Abstractions.IFileSystem interface into a class so that I can unit test file system interactions. There is one place in the class that uses new FileInfo(fileName) . What is the replacement for that when using the IFileSystem interface and MockFileSystem ?

Replacing File.OpenRead with _fileSystem.File.OpenRead is simple...

public string? Decrypt(string encryptedFilePath, string privateKeyArmor, string passPhrase)
    {
        try
        {
            using var privateKeyStream = new MemoryStream(Encoding.ASCII.GetBytes(privateKeyArmor));
            using var encryptedFileStream = _fileSystem.File.OpenRead(encryptedFilePath);

            var inputStream = PgpUtilities.GetDecoderStream(encryptedFileStream);
...

...but I don't know how to replace new FileInfo(fileName) here.

private byte[] CompressFile(string fileName, CompressionAlgorithmTag algorithm)
    {
        var outputStream = new MemoryStream();
        var compressedDataGen = new PgpCompressedDataGenerator(algorithm);
        PgpUtilities.WriteFileToLiteralData(compressedDataGen.Open(outputStream), PgpLiteralData.Binary,
            new FileInfo(fileName));
...

I tried _fileSystem.FileInfo.FromFileName(fileName) , but that returns IFileInfo instead of FileInfo and the WriteFileToLiteralData method won't take that.

Answer 1

There is a helper function FileInfo.FromFileName(string fileName) which can be used to create/use a mock IFileInfo object

public class FileInfoTest
{
    private readonly IFileSystem _fileSystem;

    public FileInfoTest()
        : this (new FileSystem())

    {
    }

    internal FileInfoTest(IFileSystem fileSystem)
    {
        _fileSystem = fileSystem;
    }

    public bool GetIsReadOnly(string path)
    {
        var info = _fileSystem.FileInfo.FromFileName(path);
        return info.IsReadOnly;
    }

}

To demonstrate this I have a physical file which is not read-only.

The first test, returns the IsReadonly state of the physical file.
The second, returns a mocked IFileInfo object with IsReadOnly set to true.

[TestMethod]
public void CheckFileInfoAgainstPhysicalFile()
{
    var tester = new FileInfoTest();
    var isReadOnly = tester.GetIsReadOnly(@"c:\dev\File.txt");
    Assert.IsFalse(isReadOnly);
}

[TestMethod]
public void CheckFileInfoAgainstMock()
{
    var mockFileInfo = new Mock<IFileInfo>();
    mockFileInfo.SetupGet(mk => mk.IsReadOnly).Returns(true);   
    var mockFileSystem = new Mock<IFileSystem>();
    mockFileSystem.Setup(mk => mk.FileInfo.FromFileName(@"c:\dev\File.txt")).Returns(mockFileInfo.Object);
        
    var tester = new FileInfoTest(mockFileSystem.Object);
    var isReadOnly = tester.GetIsReadOnly(@"c:\dev\File.txt");
    Assert.IsTrue(isReadOnly);

}